1. Field
Exemplary embodiments relate generally to a computer system and, more particularly, to a stream data processing method with multiple windows on a single stream.
2. Technical Background
Stream data processing is widely used. There has been an increasing demand for a data processing system which carries out real-time processing for data continuously arriving at a database management system (hereafter, referred to as “DBMS”). The DBMS carries out processes for data stored in a storage system.
For example, in a system for trading stocks, response time with respect to changes in stock prices is a critical factor for system users. In related art storage systems for which stock data is solely stored in the storage system, the response time of a related art DBMS method for searching through the stored data may not be sufficiently fast with respect to the actual speed of the changes in stock prices, and may result in lost business opportunities. An example related art process utilizes a mechanism which issues stored queries periodically. Therefore, it is difficult to apply such related art mechanisms to real time data processing, when it is necessary to execute a query immediately after data such as stock prices is received.
Data which continuously arrives is known in the related art as “stream data”, and related art stream data processing systems have been developed for handling real-time processing of the stream data.
In a related art stream data processing system, queries are first registered to the system, and the queries are executed continuously as data arrives, which is different from the foregoing periodic related art DBMS methods. The related art stream data processing system employs a sliding window, which partially cuts stream data and imparts a lifetime for each parsed portion of the stream data, thus efficiently processing the stream data. An example of a related art query description language including a sliding window specification is continuous query language (CQL).
The CQL includes an extension for specifying the sliding window by using parentheses following a stream name in a FROM clause of a structured query language (SQL), which is widely used for the related art DBMS. There are two types of methods in the related art for specifying the sliding window: (1) a method of specifying the number of data rows to be cut, and (2) a method of specifying a time interval containing data rows to be cut. Related art examples of method (1) involve processes in which data corresponding to 50 rows is cut to be processed. Related art examples of method (2) involve processes in which data for a time interval of 15 minutes is cut to be processed. For the related art examples of (1), the data lifetime is defined to last until 50 pieces of data arrive. For the related art examples of (2), the data lifetime is defined to last 15 minutes. The stream data cut by the sliding window is retained on a memory, and is used for the query processing.